The goal of our research is to determine the primary sequence of the envelope gly coprotein gp70 from endogenous and recombinant reteroviruses of AKR mice. We wish to define the constant and variable portions of the molecules and determine where the recombinational event takes place. Parallel studies show a correlation with the onset of leukemia and the appearance of leukemogenic recombinant viruses with alteration in their gp70s. We wish, therefore, to continue our studies of the past three years to further define the molecular alterations brought on by envelope gene recombination. Our specific aims are to continue our amino acid sequence analysis of recombinant-specific regions of AKR and Rauscher-derived recombinaant gp70s, defined in the current phase of this project. Furthermore, we wish to continue studies already initiated using monoclonal antibodies to probe the tertiary structure of parental and recombinant gp70s. These analyses include defining the cellular binding regions of gp70, mapping of highly antigenic regions, and locatlization of glycosylation sites of recombinant relative to parental virus gp70s. These studies will indicate whether specific structural changes in gp70 contribute to the unique properties of recombinant retroviruses.